1. Field of the Invention
The present invention relates to a temperature-compensated electronic watch having a temperature sensitive oscillator constructed in a MOS-IC.
2. Description of the Prior Art
In the prior art, the temperature gradient adjustor is operating with the temperature gradient adjusting numerical information only but without any roughly temperature gradient adjusting variable frequency divider interposed between the temperature sensitive oscillator and the temperature gradient adjustor.
The method of adjusting the temperature sensitive oscillator according to the prior art will be described in the following with reference to the accompanying drawings.
FIGS. 3 and 4 are block diagrams showing the basic constructions of the temperature sensitive oscillator adjusting method of the prior art.
FIG. 3 is a block diagram corresponding to the case in which the output signal frequency fs of the temperature sensitive oscillator varies linearly with the temperature, and FIG. 3 is a block diagram corresponding to the case in which the output signal period .tau.s of the temperature sensitive oscillator varies linearly with the temperature.
The temperature compensation will be described briefly with reference to FIG. 3. The temperature measurement is conducted at a constant time interval by a controller 6. When the instant for the temperature measurement comes, an offset adjusting counter 10 and a gradient adjusting counter 8 are set with adjusting numerical informations B and A, respectively, by the controller 6. Then, a latch 11 is set by the controller 6 the output signal fs of a temperature sensitive oscillator 7 begins to be inputted to the offset adjusting counter 10 via an AND gate 12. Simultaneously with this, a signal fc starts to be inputted from a frequency divider 2 to the gradient adjusting counter 8. When this gradient adjusting counter 8 is counted down by the adjusting numerical information A in response to the signal fc, a zero detector 9 conducts its zero detection to reset the latch 11 so that the AND gate 12 forbids the output signal fs of the temperature sensitive oscillator 7. As a result, the temperature information T obtained can be expressed by the following equation: EQU T=[A.fs/fc]+B-2.sup.l.m (1),
wherein EQU fs=.alpha...theta.+fo (2).
Here, letter l designates the number of bits of the offset adjusting counter 10, and letter m designates the number of times of overflows. Letter .theta. designates the temperature; letter fo designates the frequency at 0.degree. C.; and letter .alpha. designates a temperature coefficient. Symbol "[]" designates the operation to round the numeral to nearest integer.
The temperature compensation in the case of FIG. 4 is substantially the same as that in the case of FIG. 3. The temperature information T of this case can be expressed by the following equation: EQU T=[A..tau.s.fc]+B-2.sup.l.m (3),
wherein EQU .tau.s=.beta...theta.+.tau.o (4).
Here, letter .tau.o designates the period of the temperature sensitive oscillator at 0.degree. C., and letter .beta. designates a temperature coefficient.
The temperature gradient adjustors thus constructed are accompanied by a defect that the temperature gradient adjusting resolution (i.e., 1/A: the reciprocal number of the adjusting numerical information A) degrades the more as the frequency-temperature gradient or the frequency-temperature gradient of the temperature sensitive oscillator becomes the larger. In other words, the defect is that such a temperature gradient adjusting range is narrowed as can be used without any drop in the temperature gradient adjusting resolution.
The temperature gradient adjusting range will be determined in the following by substituting specific numerical values into the equations (1) and (2). If the temperature information T has a temperature depending term T.sub..theta. this term can be expressed by the following equation from the equations (1) and (2): EQU T.sub..theta. =A..alpha./fc..theta.] (5).
The upper and lower limits of the value .alpha., i.e., the temperature gradient adjusting range will be calculated by substituting an appropriate specific numerical value into the equation (5).
If a condition is set such that the temperature information T.sub..theta. is varied by 1024 for the change of the temperature .theta. of 102.4.degree. C., the following equation is obtained: EQU [A..alpha./fc]=10 (1/.degree.C.) (6).
If the gradient adjusting counter 8 is a counter of 10 bits, the adjusting numerical information A takes 10 bits. The signal fc to be used has 2048 Hz of the frequency divider.
In case the above-specified conditions are set, the adjusting numerical information A takes an integer of 0 to 1023 because of 10 bits but makes an error of 0.5 at the maximum of the adjustment because of the integer. The influences to be given to the temperature information by that error of 0.5 and the temperature gradient adjusting resolution become the larger for the smaller adjusting numerical information A. If the compensation temperature characteristics of quartz have an error not larger than 0.1 [ppm], for example, the temperature gradient adjusting resolution has to be not larger than 1/512, and the range of the adjusting numerical information A has to be from 512 to 1023. In this case, therefore, the adjustable range of the temperature gradient .alpha. is expressed by the following equation from the equation (6): EQU .alpha.=20 to 40(Hz/.degree.C.).
In case the temperature gradient .alpha. is not larger than 20 (Hz/.degree.C.), the adjusting numerical information A exceeds 1024 so that it cannot make an adjustment. In case the temperature gradient .alpha. is not larger than 40 (Hz/.degree.C.), the adjusting numerical information A becomes equal to or smaller than 511 so that the temperature gradient adjusting resolution exceeds 1/512.
If the equations (3) and (4) are calculated under absolutely the same conditions as those of the equations (1) and (2), on the other hand, the adjustable range of the temperature gradient .beta. is expressed by the following equation: EQU .beta.=4.77 to 9.54(.mu.sec/.degree.C.).
In this case, too, the adjusting numerical information A exceeds 1024 to make the adjustment impossible, if the temperature gradient .beta. becomes equal to or smaller than 4.77 (.mu.sec/.degree.C.), and becomes equal to or smaller than 511 to make the adjusting resolution equal to or more than 1/512 if the gradient .beta. exceeds 9.54 (.mu.sec/.degree.C.).
Even if the number of bits of the gradient adjusting counter 8 and the adjusting numerical information A are simply increased for widening the adjustable ranges of the temperature gradients .alpha. and .beta., another defect remains with that these widening purposes are difficult to realize partly because the time period for the temperature measurements is elongated and partly because a higher frequency has to be used as the signal.